Radio communication system, terminal and packet

ABSTRACT

A radio communication system comprises below terminals. A first radio communication terminal which is included in the plurality of radio communication terminals and stores, in a first field contained in a header of a radio communication packet, address information indicating at least one radio communication terminal to which the radio communication packet is directly transmitted. A second radio communication terminal which is included in the plurality of radio communication terminals and relays the radio communication packet with reference to the address information stored in the first field, the header of the radio communication packet including a second field which stores address information indicating a final destination terminal and a third field which stores address information indicating the first radio communication terminal as a sending source.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application is based upon and claims the benefit of priorityfrom the prior Japanese Patent Application No. 2001-304704, filed Sep.28, 2001, the entire contents of which are incorporated by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a radio communication system,terminal and packet for multihop communication.

[0004] 2. Description of the Related Art

[0005] A communication system, in which radio communication terminalsexecute communications, using another or other radio communicationterminals as repeater stations, is called a “multihop communicationsystem”. In this system, each radio communication terminal can generateand transmit information, and can also function as a repeater station.

[0006] A network that enables communications between first and secondradio communication terminals is an ad hoc network. Communicationsbetween the first terminal and a repeater terminal, between repeaterterminals, and between a repeater terminal and the second terminal arepart of the communications executed in the ad hoc network. IBSS(Independent Basic Service Set) stipulated in the IEEE802.11 local areawireless network system (ISO/TEC 8802-11:1999 (E) ANSI/IEEE Std 802.11,1999 edition) is known as a type of ad hoc network.

[0007] Referring to FIG. 1, a description will be given the IEEE802.11local area wireless network system for enabling communications betweenterminals. The local area wireless system shown in FIG. 1 is IBSS. InIBSS, a system including only two terminals (e.g. terminals 901 and 902)is a minimum system configuration.

[0008] In the ad hoc network in which communications are executedbetween a plurality of terminals, to transmit data to a destinationterminal located in a far place, there are cases where data is directlytransmitted to the destination terminal with high communication power,and where another terminal is used as a repeater station via which datais transmitted to the destination terminal. The latter case is multihopcommunication.

[0009] In general, when terminal stations are used as repeater stationsand multihop communications are executed via the terminal stations,using IBSS, four addresses are necessary, i.e., an address assigned to adestination repeater station to which a data packet is transmitteddirectly, an address assigned to an originating repeater station fromwhich the data packet is transmitted directly, an address assigned tothe final destination terminal to which the data packed is transmitted,and an address assigned to a sending source terminal by which the packetdata is generated.

[0010] However, in the conventional IBSS shown in FIG. 1, only threeaddress fields are used, and hence all the above-mentioned fouraddresses cannot be designated.

[0011] Accordingly, in a conventional radio communication terminal,address control concerning IBSS multihop communications cannot beexecuted using the MAC (Media Access Control) layer level, and hence alevel higher than the MAC level must be used to execute the addresscontrol.

BRIEF SUMMARY OF THE INVENTION

[0012] The present invention has been developed in light of the above,and aims to easily realize multihop communications based on the MAClayer level, without changing the existing basic configuration of themultihop communications but by simply adding an address control functionfor relaying a radio communication data packet.

[0013] To satisfy the aim, according to an aspect of the invention,there is provided a radio communication system in which at least one ofa plurality of radio communication terminals relays a radiocommunication packet including a header, comprising:

[0014] a first radio communication terminal which is included in theplurality of radio communication terminals and stores, in a first fieldcontained in the header of the radio communication packet, addressinformation indicating at least one radio communication terminal towhich the radio communication packet is directly transmitted; and

[0015] a second radio communication terminal which is included in theplurality of radio communication terminals and relays the radiocommunication packet with reference to the address information stored inthe first field,

[0016] the header of the radio communication packet including a secondfield which stores address information indicating a final destinationterminal and a third field which stores address information indicatingthe first radio communication terminal as a sending source.

[0017] According to another aspect of the invention, there is provided aradio communication terminal which is included in a plurality of radiocommunication terminals and can relay a radio communication packetincluding a header, comprising:

[0018] a relaying module configured to relay the radio communicationpacket with reference to address information stored in a first fieldcontained in the header of the radio communication packet, the addressinformation of the first field indicating at least one radiocommunication terminal to which the radio communication packet isdirectly transmitted,

[0019] the header of the radio communication packet including a secondfield which stores address information indicating a final destinationterminal and a third field which stores address information indicatingthe first radio communication terminal as a sending source.

[0020] According to yet another aspect of the invention, there isprovided a radio communication packet to be transmitted from a firstradio communication terminal to a second radio communication terminalvia at least one third radio communication terminal other than the firstradio communication terminal and the second radio communicationterminal, each of the first radio communication terminal, the secondradio communication terminal, and the third radio communication terminalbeing able to generate and transmit information, and also to serve as arepeater station, comprising:

[0021] a first field which stores address information indicating thethird radio communication terminal to which the radio communicationpacket is directly transmitted;

[0022] a second field which stores address information indicating thesecond radio communication terminal as a final destination terminal; and

[0023] a third field which stores address information indicating thefirst radio communication terminal as a sending source.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWING

[0024]FIG. 1 is a schematic diagram illustrating the IBSS configurationof the IEEE802.11 local area wireless network system for enablingcommunications between conventional radio communication terminals;

[0025]FIG. 2 is a schematic diagram illustrating cases where multihopcommunication is executed between radio communication terminalsaccording to embodiments of the present invention;

[0026]FIG. 3 is a block diagram illustrating a communication functionmodule housed in a radio communication terminal according to embodimentsof the present invention;

[0027]FIG. 4 is a view illustrating a structure of a data packetincluding a MAC header, employed in a first embodiment of the invention;

[0028]FIG. 5 is a flowchart illustrating address processing executed ina transmission process in the radio communication terminal of the firstembodiment if the terminal serves to generate and transmit a data packetto realize multihop communication;

[0029]FIG. 6 is a flowchart illustrating address control executed in areceiving process in the radio communication terminal of the firstembodiment if the terminal serves as a repeater station to realizemultihop communication;

[0030]FIG. 7 is a view illustrating the structure of a data packetincluding a MAC header, employed in a second embodiment of theinvention;

[0031]FIG. 8 is a flowchart illustrating address processing executed ina transmission process in the radio communication terminal of the secondembodiment if the terminal serves to generate and transmit a data packetto realize multihop communication;

[0032]FIG. 9 is a flowchart illustrating address control executed in areceiving process in the radio communication terminal of the secondembodiment if the terminal serves as a repeater station to realizemultihop communication;

[0033]FIG. 10 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a third embodiment of the invention;

[0034]FIG. 11 is a flowchart illustrating address control executed in areceiving process in a radio communication terminal according to thethird embodiment if the terminal serves as a repeater station to realizemultihop communication;

[0035]FIG. 12 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a fourth embodiment of the invention;

[0036]FIG. 13 is a view illustrating routing tables to be referred to bythe radio communication terminals of the fourth embodiment if theterminals serve as repeater stations;

[0037]FIG. 14 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a fifth embodiment of the invention;

[0038]FIG. 15 is a view illustrating a routing table to be referred toby the radio communication terminal of the fifth embodiment if theterminal serves as a repeater station;

[0039]FIG. 16 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a sixth embodiment of the invention;

[0040]FIG. 17 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a seventh embodiment of the invention;

[0041]FIG. 18 is a view illustrating the structure of a data packetincluding a MAC header, employed in the seventh embodiment of theinvention;

[0042]FIG. 19 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to an eighth embodiment of the invention;

[0043]FIG. 20 is a view illustrating the structure of a data packetincluding a MAC header, employed in the eighth embodiment of theinvention;

[0044]FIG. 21 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a ninth embodiment of the invention;

[0045]FIG. 22 is a view useful in explaining a case where when multihopcommunication is executed first by the repeater station 101, the routingtable of a radio communication terminal according to the ninthembodiment is updated using broadcasting;

[0046]FIG. 23 is a view useful in explaining another case where whenmultihop communication is executed using multicasting, the routing tableof a radio communication terminal according to the ninth embodiment isupdated;

[0047]FIG. 24 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a tenth embodiment of the invention;

[0048]FIG. 25 is a view illustrating the structure of a data packetincluding a MAC header, employed in the tenth embodiment of theinvention;

[0049]FIG. 26 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to an eleventh embodiment of the invention;

[0050]FIG. 27 is a view illustrating the structure of a data packetincluding a MAC header, employed in the eleventh embodiment of theinvention;

[0051]FIG. 28 is a view illustrating the structure of a data packetincluding a MAC header, employed in a twelfth embodiment of theinvention to obtain the number of repeater stations; and

[0052]FIG. 29 is a view illustrating the structure of a data packetincluding a MAC header, employed in the twelfth embodiment of theinvention to determine the allowable maximum number of repeaterstations.

DETAILED DESCRIPTION OF THE INVENTION

[0053] Radio communication systems, terminals, and packets according toembodiments of the inventions will be described with reference to theaccompanying drawings.

[0054]FIG. 2 is a schematic diagram illustrating cases where multihopcommunication is executed between radio communication terminalsaccording to embodiments of the present invention. In one of the casesof FIG. 2, multihop communication is executed from a terminal 201 to aterminal 203, while in the other case, multihop communication isexecuted from a terminal 204 to a terminal 207.

[0055] When multihop communication is executed from the terminal 201 tothe terminal 203, a terminal 202 serves as a repeater station. On theother hand, when multihop communication is executed from the terminal204 to the terminal 207, terminals 205 and 206 serve as repeaterstations.

[0056] As shown in FIG. 2, in multihop communication, to transmitinformation from a sending source terminal to a destination terminal,another terminal is (or other terminals are) used as a repeater station(or repeater stations) for relaying the information.

[0057]FIG. 3 is a block diagram illustrating a communication functionmodule 10 housed in a radio communication terminal according toembodiments of the present invention.

[0058] As shown in FIG. 3, the communication function module 10 housedin the radio communication terminal comprises a memory 2, basebandprocessing module 14, frequency conversion circuit 8 and radio antenna12. The baseband processing module 14 includes MAC (Media AccessControl) unit 4 and modem unit 6.

[0059] The memory 2 is connected to the MAC unit 4 for providing thecircuit with a working storage, frame buffer, etc. The MAC unit 4generates a MAC header to be attached to to-be-transmitted data, orexecutes access control for a MAC frame. The modem unit 6 connected tothe MAC unit 4 executes PLCP (Physical Layer Convergence Protocol)header processing, spread spectrum processing, phase modulationprocessing, A/D conversion, etc. The frequency conversion circuit 8connected to the modem unit 6 converts the frequency of a transmissionor received signal in a stepwise manner in order to, for example,execute internal signal processing, or emit radio waves through theradio antenna 12. The radio communication terminal constructed as abovecomplies with, for example, the IEEE802.11 local area wireless networksystem.

[0060] (First Embodiment)

[0061]FIG. 4 is a view illustrating the structure of a data packetincluding a MAC header, employed in a first embodiment of the invention.More specifically, FIG. 4 shows a structure example of a MAC headerincluded in a data packet that is employed in the IEEE802.11 local areawireless network system when terminals execute IBSS communications.

[0062] In IEEE802.11 that stipulates the physical layer and MAC (MediaAccess Control) layer, four address fields are prepared for the MACheader.

[0063] In the first embodiment, four 6-octet address fields are providedin the latter portion of the MAC header. Specifically, as shown in FIG.4, three 6-octet address fields (address 1, address 2 and address 3),and a fourth 6-octet address field (address 4) after a sequence controlfield are used.

[0064] In a network consisting of infrastructure BSSs (Basic ServiceSets) the above-described data packet structure is similar to thestructure of a data packet that is transmitted from a base station andreceived by a base station as both serving repeater stations fortransferring a data packet between terminal stations. However, thissimilar data packet structure differs from the structure of the datapacket in this embodiment in address information and BSSID written ineach address field.

[0065] More specifically, a destination address DA assigned to adestination terminal, a source address SA assigned to a sending sourceterminal that has generated and transmitted information, and BSSID as aBSS identification number are written into three address fields, i.e.,address 1, address 2 and address 3, respectively. Further, a receiveraddress RA assigned to a repeater station to which a data packetcorresponding to the information is directly transmitted is written intothe other address field, i.e., address 4.

[0066] By virtue of this structure, address control for IBSS multihopcommunication can be executed using the MAC layer level. In other words,no higher level than the MAC layer level is necessary.

[0067]FIG. 5 is a flowchart illustrating address processing executed bythe communication function module 10 of the radio communication terminalof the first embodiment if the terminal serves to generate and transmita data packet to realize multihop communication.

[0068] In the communication function module 10, when a transmission datapacket is transferred from a higher-level layer to the MAC layer, themodule 10 refers to the frame control field of the transmission datapacket, thereby determining whether or not the communication system ofthe packet is IBSS (step S1). The determination as to whether or not thecommunication system is IBSS is not necessarily executed each time adata packet is transmitted, and instead may be executed each time aplurality of data packets are transmitted.

[0069] If the communication system of a data packet is determined to beIBSS, the program proceeds to a step S2, whereas if the communicationsystem is determined not to be IBSS, the program proceeds to a step S4,where the data packet is transmitted.

[0070] If it is determined at the step S1 that the communication systemof a data packet is IBSS, it is determined whether or not the datapacket should be transmitted to a terminal with DA by multihopcommunication (step S2). If the data packet is determined to betransmitted to the terminal with DA by multihop communication, theprogram proceeds to a step S3. If, on the other hand, the data packet isdetermined not to be transmitted to the terminal with DA by multihopcommunication, the program proceeds to a step S4, where the data packetis transmitted.

[0071] If it is determined at the step S2 that the data packet should betransmitted to the terminal with DA by multihop communication, the nextterminal to which the data packet is to be transmitted is selected by arouting selection process (step S3). Subsequently, the MAC IDcorresponding to the address of the selected terminal is set as RA, a6-octet area is secured as address 4 in the MAC header of the datapacket, and RA is written into the area (step S3). After that, the datapacket is transmitted (step S4).

[0072]FIG. 6 is a flowchart illustrating address control executed in areceiving process in the radio communication terminal of the firstembodiment if the terminal serves as a repeater station to realizemultihop communication.

[0073] Upon receiving a data packet transmitted from a certain radiocommunication terminal, the radio communication terminal of the firstembodiment (i.e., the repeater station) determines whether or not itstransmission system is IBSS, referring to the frame control field of thedata packet (step S11). The determination as to whether or not thecommunication system is IBSS is not necessarily executed each time adata packet is received, and instead may be executed each time aplurality of data packets are received.

[0074] If the radio communication terminal as the repeater stationdetermines that the communication system of the received data packet isIBSS, the terminal then determines whether or not the DA contained asinformation in the data packet is identical to its MAC ID or stationitself (step S12). If the DA is identical to the MAC ID, a normalreceiving process is executed (step S13).

[0075] On the other hand, if the DA is not identical to the MAC ID, NAV(Network Allocation Vector) is usually set. However, in this embodiment,instead of setting NAV, 6-octet data contained in the MAC header of thepacket after the sequence control field is extracted as data for address4, and is used as RA (step S14). One octet includes a series of eightbits.

[0076] Thereafter, the repeater station determines whether or not the RAcontained as information in the data packet is identical to its MAC ID(step S15). If the RA is not identical to the MAC ID, the 6-octet dataextracted as RA at the preceding step is determined to be frame bodydata, and is returned to the leading part of the frame body (step S18),thereby executing a usual NAV setting process (step S19). In theembodiment of the invention, the process at the step S19 is not limitedto the NAV setting process.

[0077] If the 6-octet data set as RA at the step S15 is identical to theMAC ID of the repeater station, routing control is executed to selectthe next terminal to which the data packet is to be transmitted (stepS16). The MAC ID of the selected terminal is used as new RA, therebyupdating the 6-octet data for address 4 using the new RA (step S16), andtransmitting the data packet (step S17).

[0078] As described above, in this embodiment, the terminal, which hasreceived a data packet transmitted from the terminal that has intendedto execute IBSS multihop communication, refers to the MAC header of thedata packet to determine whether or not the terminal itself is the finaldestination terminal (step S12). If the terminal itself is not the finaldestination terminal, the terminal transfers the received data packet toanother terminal (step S17). Thus, the relay transfer of a radiocommunication data packet, i.e., multihop communication, is realized.

[0079] The operation of relaying a data packet at a terminal can beexecuted by the MAC layer level, as in the case where an infrastructureBSS base station serves as a repeater station. Accordingly, a repeaterterminal that can easily execute multihop communications can be realizedsimply by adding, to the terminal, part of the address control functionof an existing base station using the MAC layer.

[0080] Thus, the addition of the above-described additional function tothe basic function enables communications between the terminals to beprevented from interruption even if there are terminals with noadditional function coexisting with the terminals according to theembodiment in the communication system.

[0081] Specifically, if a terminal that is not in compliance withmultihop communication has received a data packet to be transmitted bymultihop communication, the terminal compares its address with theaddress (DA) of the final destination terminal in a receiving process ofthe MAC layer level (step S12). If DA is identical to the address of thesignal-received terminal, the terminal subjects the data packet to areceiving process (step S13). If, on the other hand, DA is not identicalto the address of the signal-received terminal, NAV is set (step S19).

[0082] Further, in the system including terminals compatible andincompatible with multihop communication, multihop communication can beexecuted at suppressed transmission power between the terminalsaccording to the invention, thereby reducing the degree of interferencein the entire system.

[0083] (Second Embodiment)

[0084]FIG. 7 is a view illustrating the structure of a data packetincluding a MAC header, employed in a second embodiment of theinvention.

[0085] In the second embodiment, elements different from those of thefirst embodiment will be mainly described. The second embodiment differsfrom the first embodiment in that an address TA (Transmitter Address)assigned to a terminal from which the data packet is directlytransmitted is written, instead of the conventional BSSID, into thefield of address 3 in the data packet structure for multihopcommunication of the first embodiment shown in FIG. 4.

[0086]FIG. 8 is a flowchart illustrating address processing executed ina transmission process in a radio communication terminal according tothe second embodiment if the terminal serves to generate and transmit adata packet to realize multihop communication.

[0087] In this embodiment, in accordance with the writing of the addressTA, address processing (step S20) for also writing TA in addition to RAis added to the processing executed in the transmission process in thefirst embodiment shown in FIG. 5.

[0088] Specifically, if it is determined at the step S2 that the datapacket is to be transmitted to the terminal with DA using multihopcommunication, the address of this terminal is written as the TA (stepS20). After that, the program proceeds to a step S3. The other steps aresimilar to the address processing steps in the first embodiment.

[0089]FIG. 9 is a flowchart illustrating address control executed in areceiving process in the radio communication terminal of the secondembodiment if the terminal serves as a repeater station to realizemultihop communication.

[0090] In this embodiment, in accordance with the writing of the addressTA to the address field, if the 6-octet data subsequent to the sequencecontrol field is determined to be RA in the receiving process at therepeater station of the first embodiment, it is determined that the datain the address 3 field is not BSSID but TA.

[0091] Specifically, the 6-octet data subsequent to the sequence controlfield of the MAC header of the received data packet is extracted as thefield data of address 4 at the step S14, and the extracted address fielddata is set as RA. Thereafter, the field data of address 3 is determinedto be TA. The order of extracting RA and determining TA may be reversed.The other steps are similar to the address control steps in the firstembodiment.

[0092] Thereafter, a terminal (a repeater station) executes a processfor selecting a route to a final destination terminal indicated by DA.If a determination result that indicates that a repeater station otherthan the present repeater station is preferable is obtained, the resultis reported to the terminal that has this TA as MAC ID and is thetransmitter of the received data packet. Upon receiving the report, thetransmitter terminal feeds the report back to its routing selectionprocess.

[0093] If the transmitter terminal that has transmitted the data packetto the repeater station using multihop communication, and is indicatedby TA as the address 3 field data of the MAC header of the data packet,receives, from the repeater station, a report indicating that it ispreferable to use a repeater station other than the present repeaterstation, and feeds the report back to its route selection process, thetransmitter terminal may supply information indicating that the terminalhas executed a feedback operation, to the preceding terminal indicatedby TA as the address 3 field data of the MAC header of the data packetreceived by the transmitter terminal.

[0094] As described above, the writing of TA to the field of address 3of the MAC header of a data packet to be transmitted by multihopcommunication enables the feedback of the result of the routingselection process executed by a repeater station, to the terminaltransmitted the data packet and also to the terminal previous to theterminal that transmitted the packet. As a result, the routing table canbe updated in accordance with the movement of terminals or change inradio propagation circumstances.

[0095] (Third Embodiment)

[0096] A third embodiment will be described. In this embodiment, adescription will be mainly given of the points different from the firstembodiment. The third embodiment differs from the first embodiment inthat the third embodiment employs multihop communication in which theaddress assigned to a terminal, to which data are to be transmittedfinally, has to be a unicast address.

[0097]FIG. 10 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to the third embodiment of the invention.

[0098] As shown in FIG. 10, in the case of communication using a unicastaddress, there exists only one destination address (DA) for a datapacket. In the case of FIG. 10, a data packet is transmitted from arepeater station 101 to a repeater station 103, and then from therepeater station 103 to a repeater station 104 that is DA.

[0099]FIG. 11 is a flowchart illustrating address control executed in areceiving process in a radio communication terminal according to thethird embodiment if the terminal serves as a repeater station to realizemultihop communication.

[0100] Also in this embodiment, it is first determined whether or notthe system is IBSS (step S11), as in the address control process in thereceiving process, executed by a terminal serving as a repeater stationin the first embodiment shown in FIG. 6. If it is determined to be IBSS,it is determined whether or not DA is identical to the MAC ID of therepeater station (step S12).

[0101] If it is determined at the step S12 that DA is not identical tothe MAC ID of the repeater station, it is first determined in thisembodiment whether or not the field data DA of address 1 of the MACheader indicates group address information (step S22). “Group address”in general is an address indicating a plurality of addresses as one. Ifit is determined at the step S22 that the field data DA of address 1indicates group address information, it is determined that the datapacket does not contain a field for address 4, and the program promptlyshifts to the NAV setting process (step S23).

[0102] If, on the other hand, the field data DA of address 1 does notindicate group address information, the program proceeds to a step S14.The other steps are similar to the address control steps in the firstembodiment.

[0103] In the above-described third embodiment, it can be easilydetermined whether or not the data packet uses multihop communication.If the data packet does not use multihop communication, the programpromptly shifts to a usual receiving process (for example, NAV settingprocessing).

[0104] The generating and updating of a routing table applicable to theabove-described first to third embodiments will be described withreference to fourth to ninth embodiments.

[0105] (Fourth Embodiment)

[0106]FIG. 12 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a fourth embodiment of the invention.

[0107] When a repeater station 101 in the IBSS system has transmitted abeacon signal with a predetermined transmission power that falls withina range allowable in the system, repeater stations 102 and 103 receivethe beacon signal from the repeater station 101. Each repeater stationreceived the beacon signal records, in its routing table, that eachrepeater station can execute direct communication with the repeaterstation 101.

[0108]FIG. 13 is a view illustrating routing tables to be referred to bythe radio communication terminals of the fourth embodiment if theterminals serve as repeater stations.

[0109] Each routing table stores an address (DA) assigned to the finaldestination repeater station, an address (RA) assigned to a directdestination repeater station, accessible stations, and the receptionlevels of beacon signals from the accessible stations.

[0110] In the case of FIG. 12, when the repeater stations 102 and 103have received a beacon signal from the repeater station 101, the number101 is written to the column for accessible stations in each routingtable of the repeater stations 102 and 103. Further, whether or not thelevel of the received beacon signal is high is also written to eachrouting table of the repeater stations 102 and 103.

[0111] As a result, when the repeater station 102 or 103 has received adata packet related to multihop communication, each repeater station canuse the repeater station 101 as a candidate for a repeater station towhich the data packet is to be transmitted next.

[0112] Further, if the repeater station 102 has transmitted a beaconsignal of a predetermined transmission power level like the repeaterstation 101, the repeater stations 101 and 104 receive the beacon signalfrom the repeater station 102. The repeater stations 101 and 104 record,in their respective routing tables, the fact that they can directlycommunicate with the repeater station 102, as shown in FIG. 13.

[0113] Through the above-described procedure, each repeater stationupdates a routing table that shows a destination repeater station orstations with which each repeater station can communicate in IBSS.

[0114] Moreover, when the repeater station 101 has transmitted itsrouting table to the repeater station 102, the repeater station 102knows that it can also communicate with the repeater station 103. If therepeater station 102 would like to transmit information to the repeaterstation 103, the station 102 records, in its routing table, that therepeater station 101 can be a candidate for a repeater station as isshown in FIG. 13.

[0115] By transmitting a routing table to another directly accessiblerepeater station, each repeater station increases the amount ofinformation concerning destination repeater stations with which eachrepeater station can communicate, thereby updating its routing table.

[0116] Each repeater station equipped with a routing table generated andupdated as described above can appropriately select the next repeaterstation when the station generates a data packet for transmitting orrelays a data packet using multihop communication.

[0117] (Fifth Embodiment)

[0118] In a fifth embodiment, the above-described routing table isupdated based on a process on an authentication signal.

[0119]FIG. 14 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to the fifth embodiment of the invention.

[0120] As shown in FIG. 14, the reliability of the communication channelbetween the repeater stations 101 and 102 is enhanced if the repeaterstation 101 gives authentication to the repeater station 102. In therouting table of, for example, the repeater station 101, thiscommunication channel has a higher priority than the communicationchannel between the repeater stations 101 and 103 with noauthentication.

[0121] For example, when a data packet is transmitted from the repeaterstation 101 to the repeater station 105 using multihop communication,there are two routes that depend upon whether the data packet is relayedby the repeater station 102 or 103. In this case, the repeater station102 to which authentication was given is selected as the next repeaterstation.

[0122]FIG. 15 is a view illustrating a routing table to be referred toby the radio communication terminal of the fifth embodiment if theterminal serves as a repeater station. This routing table belongs to therepeater station 102.

[0123] When the repeater station 102 has received a data packet that isrelated to multihop communication and directed from the repeater station104 to the repeater station 103, if the repeater station 102 has arouting table in which the communication channel between the repeaterstations 101 and 102 is set to have a higher priority, or if therepeater station 101 has given authentication to the repeater station102 as described above, the repeater station 102 chooses the repeaterstation 101 in preference to the repeater station 105.

[0124] In the above-described fifth embodiment, multihop communicationscan be realized according to the reliability of the relay communicationchannel, using the routing table.

[0125] (Sixth Embodiment)

[0126] In a sixth embodiment, the processing result of exchanging an RTS(Request to Send) signal and a CTS (Clear to Send) signal betweenrepeater stations updates the routing table of each of the repeaterstation.

[0127]FIG. 16 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to the sixth embodiment of the invention.

[0128] When, for example, the repeater station 101 has transmitted anRTS signal to the repeater station 103 and the repeater station 103 hasreceived the signal as shown in FIG. 16, the repeater station 103transmits a CTS signal corresponding to the RTS signal to the repeaterstation 101. In this case, if the repeater station 103 cannot receivethe RTS signal from the repeater station 101 because one or both of therepeater stations have moved or the radio propagation circumstancesbetween the repeater stations 101 and 103 have changed for some reason,the repeater station 101 determines that no CTS signal has beentransmitted from the repeater station 103 after waiting for the CTS fora predetermined period of time. Further, the repeater station 101updates the routing table by deleting the repeater station 103 from thedirectly accessible terminal candidates specified therein, or reducingthe degree of priority of the communication channel to the repeaterstation 103. The repeater station 101 determines that no CTS signal hasbeen transmitted from the repeater station 103 and updates the routingtable in the same when the CTS signal transmitted from the repeaterstation 103 cannot be received by the repeater station 101. On the otherhand, when the exchange of RTS and CTS signals succeeded, the priorityof the communication channel between the repeater station 101 and 103 isgiven high in the routing table of repeater station 101.

[0129] The thus-updated routing table of the repeater station 101 can betransmitted from the repeater station 101 to the repeater station 102 sothat the routing table of the repeater station 102 can also be updated.The sixth embodiment described above has the same advantage as that ofthe fifth embodiment.

[0130] (Seventh Embodiment)

[0131]FIG. 17 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to a seventh embodiment of the invention.

[0132] When a broadcast address is written as RA at the repeater station101, the radio waves generated from the repeater station 101 can bereceived and relayed by any repeater station that the waves havereached.

[0133] If a routing table has just been generated and hence does notstore any information on terminals or information used to transmit orrelay a data packet related to multihop communication to the finaldestination terminal, the terminal of this embodiment is arranged towrite a broadcast address to the data field of address 4 assigning anaddress to the next terminal, as shown in FIG. 18. For example, thenumber 1 is written as the broadcast address to all bits of the datafield of address 4.

[0134]FIG. 18 is a view illustrating the structure of a data packetincluding a MAC header, employed in the seventh embodiment of theinvention.

[0135] This structure makes it possible for a generated data packet(related to multihop communication) having possibility of reaching thefinal destination terminal even if none of the terminals in the radiocommunication system have completely closed routing tables.

[0136] It is a matter of course that the processing according to theseventh embodiment may be executed even if a routing table has beengenerated or updated as in the above-described fourth to sixthembodiments.

[0137] (Eighth Embodiment)

[0138]FIG. 19 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to an eighth embodiment of the invention.

[0139] In the fourth to sixth embodiments, when a repeater stationselects, using a routing table, the next repeater station in order totransmit a data packet related to multihop communication to the finaldestination repeater station, there is a case where a single candidaterepeater station cannot be selected, i.e., there exist a plurality ofcandidate repeater stations, because the stations have the same or closeselection conditions.

[0140]FIG. 19 shows a case where a data packet is transmitted from therepeater station 101 to the repeater station 105 via the repeaterstations 102 and 103.

[0141] In this case, as shown in FIG. 20, addresses assigned to aplurality of candidate repeater stations are written in the form ofmulticast address information to the data field of address 4 assigningan address RA to the next terminal.

[0142]FIG. 20 is a view illustrating the structure of a data packetincluding a MAC header, employed in the eighth embodiment of theinvention.

[0143] This structure enables the transmission of a data packet relatedto multihop communication via a plurality of channels. Therefore thedata packet can be more reliably transmitted to the final destinationrepeater station.

[0144] (Ninth Embodiment)

[0145] When a data packet related to multihop communication, the datapacket being transmitted or relayed by broadcasting, has reached thefinal destination repeater station in the seventh embodiment, the finaldestination repeater station, in turn, generates and transmits a newdata packet related to multihop communication to the originatingrepeater station as a sending source. This data packet reaches theoriginating repeater station through the reverse channel or route.

[0146]FIG. 21 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to the ninth embodiment of the invention.

[0147] In the case of FIG. 21, the data packet transmitted from therepeater station 101 as the sending source reaches the repeater station105 as the final destination repeater station via the repeater station102. As an example of reverse routing, the data packet transmitted fromthe repeater station 105 reaches the repeater station 101 via therepeater station 103.

[0148] As a result, when a repeater station that once generated orrelayed a data packet related to multihop communication to the finaldestination repeater station again transmits a data packet to the samefinal destination repeater station, the station can select a single or aplurality of candidates as the next repeater station based on theinformation concerning another data packet reached the station throughthe reverse route, thereby updating the routing table of the repeaterstation.

[0149]FIG. 22 is a view useful in explaining a case where, when multihopcommunication is executed first by the repeater station 101, the routingtable of a radio communication terminal according to the ninthembodiment is updated using broadcasting.

[0150] The data packets which reach the repeater station 101 through thecommunication channel from the repeater stations 102 and 103 shown inFIG. 21 also give receiving information (e.g. receiving levelinformation) from the repeater stations 102 and 103 to the repeaterstation 101. On the basis of the receiving information, the routingtable of the repeater station 101 is updated as shown in FIG. 22. It isunderstood from this routing table that if the final destinationrepeater station is the repeater station 105, further stable datacommunication can be realized by selecting the repeater station 103 (notthe repeater station 102) for relaying data packets.

[0151] The above-described ninth embodiment enables a more complicatedcommunication channel network related to multihop communication to beemployed.

[0152] Also, in the eight embodiment, when a data packet related tomultihop communication transmitted or relayed using multicast addressinformation has reached the final destination repeater station, thefinal destination repeater station may generate and transmit a new datapacket to the sending source terminal, as in the above-described caseusing broadcast address information. This data packet reaches thesending source terminal through the reverse route.

[0153] As a result, when a repeater station, which once generated orrelayed a data packet related to multihop communication to the finaldestination repeater station, again transmits a data packet to the samefinal destination repeater station, the station can select a single or aplurality of candidates for the next repeater station based on theinformation concerning another data packet reached there through thereverse route, thereby updating the routing table of the repeaterstation.

[0154]FIG. 23 is a view useful in explaining another case where whenmultihop communication is executed first using multicasting by therepeater station 101, the routing table of a radio communicationterminal according to the ninth embodiment is updated.

[0155] As in the case of multihop communication where the repeaterstation 101 first uses broadcasting, the data packets which reach therepeater station 101 from the repeater stations 102 and 103 also givereceiving information (e.g. receiving level information) from therepeater stations 102 and 103 to the repeater station 101. On the basisof the receiving information, the routing table of the repeater station101 is updated as shown in FIG. 23. In the previous routing table beforebeing updated, the receiving level of each repeater station 102 or 103is low for the repeater station 101. However, it is understood now fromthe updated routing table that if the final destination repeater stationis the repeater station 105, further stable data communication can berealized by selecting the repeater station 103 (not the repeater station102) for relaying a data packet. Since the communication circumstancesof radio waves change every second, a routing table more suitable forthe present circumstances than the previous one can be obtained by theupdating process.

[0156] If this configuration of the ninth embodiment is combined withthe aforementioned configuration, a further complicated communicationchannel network related to multihop communication can be employed.

[0157] (Tenth Embodiment)

[0158] A tenth embodiment is obtained by adding a field for storing thenumber of repeater stations to the data packet employed in each of thefourth to sixth embodiments.

[0159]FIG. 24 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication terminalsaccording to the tenth embodiment of the invention.

[0160] In FIG. 24, when the repeater station 101 transmits a data packetto the repeater station 104 as the final destination, suppose that therepeater station 102 is used to relay the data packet. In this case, ifthe repeater station 102 transmits the data packet to the repeaterstation 104, and the repeater station 104 has received the data packetsuccessfully, the repeater station 104 can know that only one repeaterstation (102) has been used to relay the data packet, from the fact thatthe data in the field for storing the number of repeater stationsindicates 1.

[0161] On the other hand, if the repeater station 101 first selects therepeater station 103 as a station for relaying the data packet, it isnecessary to use another repeater station (e.g., the repeater station105) since no data packet can be transmitted directly from the repeaterstation 103 to the repeater station 104.

[0162] In this case, when the repeater station 104 has received the datapacket transmitted from the repeater station 101 and relayed by therepeater station 105, the station 104 can know from the packet that thenumber of required repeater stations is 2.

[0163] Therefore, if the repeater station 104 conversely transmits adata packet related to multihop communication to the repeater station101 as the final destination, the station 104 can select the repeaterstation 102 as the next station in order to select the communicationchannel interposed with the fewest repeater stations between therepeater stations 104 and 101.

[0164]FIG. 25 is a view illustrating the structure of a data packetincluding a MAC header, employed in the tenth embodiment of theinvention.

[0165] As shown in FIG. 25, the number of repeater stations is writtento the repeater station field. This number indicates the total number ofrepeater stations through which the data packet has been relayed so far.For example, in FIG. 24, concerning a data packet transmitted from therepeater station 101 to the repeater station 104 via the repeaterstation 102, the total number of repeater stations is 1 (i.e., therepeater station 102). Further, in FIG. 24, concerning a data packettransmitted from the repeater station 101 to the repeater station 104via the repeater stations 103 and 105, the total number of repeaterstations is 2 (i.e., the repeater stations 103 and 105).

[0166] For example, when the repeater station 101 transmits a datapacket to the repeater station 104 as the final destination, if thestation 101 cannot determine which one of the two terminals (i.e., therepeater stations 102 and 103) stored in its routing table should beselected, the station 101 transmits the data packet by inputtingmulticast address information as the address 4 of the packet.

[0167] As described above, if the repeater station 104 has received,from the repeater station 102, a data packet storing 1 as the totalnumber of required repeater stations, and received, from the repeaterstation 105, a data packet storing 2 as the total number, the repeaterstation 104 transmits a response frame to the repeater station 101,designating the repeater station 102 as a station for relaying the datapacket. Upon receiving the response frame, the repeater station 101stores the frame in its routing table as information indicating that therepeater station 102 should be used next time as a station for relayinga data packet to the repeater station 104 as the final destination.

[0168] Further, if the repeater station 104 is used to relay a datapacket from the repeater station 101 as the sending source, and hasreceived, from the repeater stations 102 and 105, data packets whichcontain the same information except for the data in the repeater stationfield, the station 104 compares the data items in the repeater stationfield, thereby stopping the relay of the data packet in which therepeater station field stores data indicating a larger number. Thisprevents increases in the communication of data packets that contain thesame information and differ only in communication channel.

[0169] (Eleventh Embodiment)

[0170] An eleventh embodiment is directed to the case of setting theupper limit for the number of repeater stations that can relay a datapacket generated by a sending source repeater station.

[0171]FIG. 26 is a schematic diagram illustrating a case where multihopcommunication is executed between radio communication repeater stationsaccording to the eleventh embodiment of the invention.

[0172] In FIG. 26, suppose that the allowable maximum number of repeaterstations is 2 in the above-described embodiment. In the above-describedembodiment, when the repeater station 101 transmits a data packetrelated to multihop communication to the repeater station 104 as thefinal destination and the repeater station 101 cannot determine whichterminal should be used as a station for relaying the data packet,multicast or broadcast address information is written to the field ofaddress 4 of the data packet. Also the allowable maximum number ofrepeater stations, 2, is written in the repeater station field in theMAC header of the data packet. The field of writing down this allowablemaximum number of repeater stations is described latter using FIG. 27.

[0173] If the repeater station 103 that has received the data packetfrom the repeater station 101 does not contain, in its routing table,information on the repeater station 104, the station 103 cannotdetermine which repeater station should be used as the next repeaterstation. In this case, the repeater station 103 inputs group addressinformation as multicast or broadcast address information, and rewritesthe allowable maximum number of repeater stations as “1”. This number isobtained by subtracting 1 (corresponding to the repeater station 103itself) from the number in the repeater station field. After that, therewritten data packet is transmitted.

[0174] Similarly, if a repeater station 106 that has received the datapacket from the repeater station 103 has no information concerning therepeater station 104, the station 106 writes group address informationinto the data field of address 4 and rewrites the allowable maximumnumber of repeater stations as “0”. This number is obtained bysubtracting 1 (corresponding to the repeater station 106 itself) fromthe number in the repeater station field. Thereafter, the rewritten datapacket is transmitted. If a repeater station other than the repeaterstation 104 has received this data packet that contains allowablemaximum number of “0”, the data packet cannot be further relayed andhence the relay operation is stopped.

[0175]FIG. 27 is a view illustrating the structure of a data packetincluding a MAC header, employed in the eleventh embodiment of theinvention.

[0176]FIG. 27 shows a case where the allowable maximum number ofrepeater stations written in the repeater station field. When thisallowable maximum number of repeater stations is initially set as 2, thedata packet transmitted from a sending source repeater terminal can berelayed by the repeater stations twice including the transmission of thesending source repeater station.

[0177] Each time a data packet transmitted from the sending sourcerepeater station passes through a repeater station, “1” is subtractedfrom the value written in the repeater station field. For example, ineach data packet transmitted from the sending source repeater station101, “2” as the initial allowable maximum number is written in therepeater station field. After this data packet is relayed by therepeater station 103, the data in the repeater station field is changedto “1”. If the repeater station 106 has received the data packet andconfirms, from the comparison of its MAC ID with the data packet, thatthe repeater station 106 is not the final destination, the station 106executes no further relaying operation.

[0178] As described above, in the eleventh embodiment, if, for example,the routing from the sending source terminal to the final destinationterminal is not established, proliferation of a data packet throughoutthe system is prevented. That is to say, substantially endless relayingof a data packet transmitted from the sending source terminal isprevented. The endless relaying occurs when the data packet is passedthrough a plurality of communication channels and relayed again andagain without finding the final destination station.

[0179] (Twelfth Embodiment)

[0180] A twelfth embodiment is a combination of the tenth and eleventhembodiments. In the twelfth embodiment, the number of repeater stationsis detected, and the relaying operation is stopped based on theallowable maximum number of repeater stations. In the tenth embodiment,the sending source terminal defines the allowable maximum number ofrepeater stations and writes the number into the repeater station fieldof a data packet when the terminal transmits the data packet.

[0181] A reference value is provided for the field that stores thenumber of repeater stations. Both the operation executed during a relayoperation in order to detect the number of repeater stations, and theoperation executed during a relay operation when the allowable maximumnumber of repeater stations is defined are performed by a single manner.

[0182] In this embodiment, the reference value for the repeater stationfield is set, for example, to “0”, and the value in the repeater stationfield is incremented by 1 each time a relaying operation is executed. Inthis case, the terminal received a data packet determines that thepresent communication is executed for detecting the number of repeaterstations, thereby relaying the data packet, if the value of the repeaterstation field of the data packet is higher than or equal to 0, i.e., thevalue is positive or 0. On the other hand, if the value is lower than 0,i.e., the value is negative, the terminal determines that the datapacket has been transmitted with the allowable maximum number ofrepeater stations defined. The relay of the data packet is stopped ifthe value reaches 0. In other case, that is, the case that the referencevalue for the repeater station field is 0 is described after.

[0183]FIG. 28 is a view illustrating the structure of a data packetincluding a MAC header, employed in the twelfth embodiment of theinvention to obtain the number of repeater stations.

[0184] The repeater station field shown in FIG. 28 is written a number.The number written in the field indicates the total number of repeaterstations through which the data packet has been relayed so far, or theallowable maximum number of repeater stations. FIG. 28 shows a casewhere the reference value 0 is written in the field. If the referencevalue higher than 0 or equal to 0, the reference number corresponds tothe total number of repeater stations through which the data packet hasbeen relayed so far.

[0185] When a sending source terminal transmits a data packet to detectthe number of repeater stations, the initial value of the repeaterstation field is set to 0. Each repeater station increments, by 1, thevalue of the repeater station field when the station relays the datapacket. As a result, each repeater station and the final destinationterminal can detect the number of repeater stations existing betweenitself and the sending source terminal.

[0186]FIG. 29 is a view illustrating the structure of a data packetincluding a MAC header, employed in the twelfth embodiment of theinvention to determine the allowable maximum number of repeaterstations.

[0187] When a sending source terminal transmits a data packet, with theallowable maximum number of repeater stations defined in the terminal,this number is written as a negative value in the repeater stationfield. Each repeater station received the data packet increments thevalue of the repeater station field by 1. If the routing table of eachrepeater station does not store the address of the final destinationterminal, each repeater station may stop the relay operation.

[0188] When defining the allowable maximum number of repeater stationsfrom the optimal number of repeater stations in order to stop therelaying operation, it is preferable that the absolute value of theallowable maximum number is set to a value slightly higher (e.g., by 1)than the required value. This is because even if the final destinationterminal is not stored in the routing table, it is possible that thefinal destination terminal may be included in the next repeater stationsaccessed using group address information.

[0189] If a repeater station received the data packet detects that thevalue of its repeater station field is 0, it determines that the datapacket has been transmitted to detect the number of repeater stations.If a repeater station received the data packet detects that the value ofthe repeater station field is −1, it determines that the data packet hasbeen transmitted with the limitation of the allowable maximum number ofrepeater stations and the relay of the data packet is stopped.

[0190] Even when the previous repeater station did not stop relaying thedata packet in the later case and relayed the data packet rewriting itsrepeater station field as 0 by incrementing by 1, and the data packet isreceived at the next repeater station, if TA is stored in the field ofaddress 3 as in the second embodiment, this data can be used for theabove determination. If TA in the field of address 3 differs from SA inthe field of address 2, it is determined that the value 0 in therepeater station field is obtained by adding “1” to the previous value.In other words, if TA in the field of address 3 differs from SA in thefield of address 2, it is determined that the data packet has beentransmitted with the allowable maximum number of repeater stationsdefined.

[0191] In the above-described twelfth embodiment, the optimal number ofrepeater stations existing from the sending source terminal to anyoptionally selected final destination terminal can be detected. Further,the allowable maximum number of repeater stations can be also set, for adata packet to be transmitted to another final destination terminal,referring to the detected number.

[0192] The advantages obtained from the above-described first to twelfthembodiments will now be described.

[0193] In communications between IBSS terminals, multihop communicationcan be realized additionally using the relay function employed in a BSSbase station. This additional function can be easily mounted by the MAClayer level control, and is effective for making the terminals executemultihop communication promptly. The addition of the function to thebasic function employed in the IBSS communication prevents interruptionof communication in a system including terminals that do not correspondto the embodiments of the present invention. Further, when multihopcommunication is executed between terminals according to the embodimentsof the invention in the system, the transmission power used in themultihop communication can be suppressed, thereby reducing the degree ofinterference in the entire system.

[0194] Moreover, the writing of TA in a data packet transmitted usingmultihop communication enables the result of a routing selection processexecuted by a repeater station to be fed back to the preceding repeaterstation transmitted the data packet, and to be also fed back to thefurther previous repeater stations. Accordingly, the routing table canbe updated in accordance with changes in the position of each repeaterstation or radio propagation circumstances.

[0195] Also, in the case of multihop communication in which the addressof the final destination station is set using unicast addressinformation, if it is determined, in the step executed to determineaddress information during a receiving process by a terminal serving asa repeater station, that the terminal is an IBSS terminal, and DA doesnot correspond to the address of the repeater station, and the addressinformation is group address information, then the data packet receivedis determined not to be multihop data packet, and the process is shiftedto the NAV setting process. This simplifies the process executed by theterminal that has received a data packet.

[0196] Further, since each terminal generates and updates its ownrouting table, it can select, based on the routing table, the nextterminal to which a multihop data packet is relayed or transmitted.

[0197] Where each terminal has its own routing table, the reliability ofthe routing tables can be enhanced by exchanging data packets concerningauthentication. This enables selection of a more reliable communicationchannel from a plurality of communication channels, if the plurality ofcommunication channels exists, thereby realizing reliable multihopcommunication.

[0198] Furthermore, RTS and CTS signals may be exchanged. This alsoenhances the reliability of the routing table and hence realizesreliable multihop communication.

[0199] The writing of broadcast address information into the field ofaddress 4 enables a generated multihop data packet to reach a finaldestination terminal, even if the routing tables of all the terminalsare not completely closed.

[0200] If a routing table stores a plurality of candidates for the nextterminal, the writing of multicast address information to the field ofaddress 4 enables a multihop data packet to be transmitted via aplurality of communication channels. This means that the data packet canbe transmitted to the final destination terminal more reliably.

[0201] Also, when the terminal that has generated or relayed a multihopdata packet transmits the data packet to the final destination terminal,the terminal can reduce, to, for example, one, the number of candidatesfor the next terminal based on information reached there through thereverse routing, thereby updating its own routing table.

[0202] The provision of a field in a multihop data packet, in which thenumber of repeater stations is written, and the input of informationindicating the number into the routing table of each terminal enablesthe selection of a route with a lower number of repeater stations.

[0203] In addition, the transmission of a multihop data packet with theallowable maximum number of repeater stations defined preventsproliferation, within the communication system, of the data packet,which occurs when the data packet is passed through a plurality ofcommunication channels and relayed again and again because of, forexample, the routing from the sending source terminal to the finaldestination terminal is not established.

[0204] Furthermore, the optimal number of repeater stations to eachfinal destination terminal can be detected, and further, the allowablemaximum number of repeater stations can be also set for a data packet tobe transmitted to another final destination terminal, referring to thedetected number.

[0205] The invention is not limited to the above-described embodiments,but may be modified in various ways without departing from its scope.

[0206] Additional advantages and modifications will readily occur tothose skilled in the art. Therefore, the invention in its broaderaspects is not limited to the specific details and representativeembodiments shown and described herein. Accordingly, variousmodifications may be made without departing from the spirit or scope ofthe general inventive concept as defined by the appended claims andtheir equivalents.

What is claimed is:
 1. A radio communication system in which at leastone of a plurality of radio communication terminals relays a radiocommunication packet including a header, comprising: a first radiocommunication terminal which is included in the plurality of radiocommunication terminals and stores, in a first field contained in theheader of the radio communication packet, address information indicatingat least one radio communication terminal to which the radiocommunication packet is directly transmitted; and a second radiocommunication terminal which is included in the plurality of radiocommunication terminals and relays the radio communication packet withreference to the address information stored in the first field, theheader of the radio communication packet including a second field whichstores address information indicating a final destination terminal and athird field which stores address information indicating the first radiocommunication terminal as a sending source.
 2. The radio communicationsystem according to claim 1, wherein the header of the radiocommunication packet further includes a fourth field which storesaddress information indicating at least one radio communication terminalfrom which the radio communication packet is directly transmitted. 3.The radio communication system according to claim 1, wherein the secondradio communication terminal extracts the address information from thefirst field of the radio communication packet, determines, based on theaddress information extracted, whether or not the second radiocommunication terminal is an immediate destination to which the radiocommunication packet is transmitted, updates the address information inthe first field, and then transmits the radio communication packet whichincludes the address information updated to at least remaining one ofthe radio communication terminals when the second radio communicationterminal determines to be the immediate destination.
 4. The radiocommunication system according to claim 1, wherein the addressinformation stored in the first field includes group address informationwhich contains at least one address information.
 5. The radiocommunication system according to claim 1, wherein the addressinformation stored in the second field includes group addressinformation which contains at least one address information.
 6. Theradio communication system according to claim 1, wherein the secondradio communication terminal is selected from a routing table whichcontains at least the address information.
 7. The radio communicationsystem according to claim 6, wherein the routing table includesinformation indicating reliability of communication between the firstradio communication terminal and the second radio communicationterminal.
 8. The radio communication system according to claim 6,wherein the routing table is updated by exchanging the radiocommunication packet between the first radio communication terminal andthe second radio communication terminal.
 9. The radio communicationsystem according to claim 6, wherein the routing table is updated basedon a received level of the radio communication packet.
 10. The radiocommunication system according to claim 6, wherein the routing tableincludes information which is based on a sum of the radio communicationterminals which have relayed the radio communication packet.
 11. Theradio communication system according to claim 10, wherein relayoperation that the radio communication packet is relayed is stopped inaccordance with the information which is based on a sum of the radiocommunication terminals which have relayed the radio communicationpacket.
 12. A radio communication terminal which is included in aplurality of radio communication terminals and can relay a radiocommunication packet including a header, comprising: a relaying moduleconfigured to relay the radio communication packet with reference toaddress information stored in a first field contained in the header ofthe radio communication packet, the address information of the firstfield indicating at least one radio communication terminal to which theradio communication packet is directly transmitted, the header of theradio communication packet including a second field which stores addressinformation indicating a final destination terminal and a third fieldwhich stores address information indicating the first radiocommunication terminal as a sending source.
 13. The radio communicationterminal according to claim 12, wherein the header of the radiocommunication packet further includes a fourth field which storesaddress information indicating at least one radio communication terminalfrom which the radio communication packet is directly transmitted. 14.The radio communication terminal according to claim 12, furthercomprising: an extracting module configured to extract the addressinformation from the first field of the radio communication packet; adetermining module configured to determine, based on the addressinformation extracted, whether or not the radio communication terminalis an immediate destination to which the radio communication packet istransmitted; and an updating module configured to update the addressinformation in the first field and then transmits the radiocommunication packet which includes the address information updated toat least remaining one of radio communication terminal when the radiocommunication terminal determines to be the immediate destination. 15.The radio communication terminal according to claim 12, wherein theaddress information stored in the first field includes group addressinformation which contains at least one address information.
 16. Theradio communication terminal according to claim 12, wherein the addressinformation stored in the second field includes group addressinformation which contains at least one address information.
 17. Theradio communication terminal according to claim 12, wherein the radiocommunication terminal to which the radio communication packet isdirectly transmitted is selected from a routing table which contains atleast the address information.
 18. The radio communication terminalaccording to claim 17, wherein the routing table includes informationindicating reliability of communication between the radio communicationterminal and at least remaining one of radio communication terminals.19. The radio communication terminal according to claim 17, wherein therouting table is updated by exchanging the radio communication packetbetween the radio communication terminal and at least remaining one ofradio communication terminals.
 20. The radio communication terminalaccording to claim 17, wherein the routing table is updated based on areceived level of the radio communication packet.
 21. The radiocommunication terminal according to claim 17, wherein the routing tableincludes information which is based on a sum of the radio communicationterminals which have relayed the radio communication packet.
 22. Theradio communication terminal according to claim 21, wherein relayoperation that the radio communication packet is relayed is stopped inaccordance with the information which is based on a sum of the radiocommunication terminals which have relayed the radio communicationpacket.
 23. A radio communication packet to be transmitted from a firstradio communication terminal to a second radio communication terminalvia at least one third radio communication terminal other than the firstradio communication terminal and the second radio communicationterminal, each of the first radio communication terminal, the secondradio communication terminal, and the third radio communication terminalbeing able to generate and transmit information, and also to serve as arepeater station, comprising: a first field which stores addressinformation indicating the third radio communication terminal to whichthe radio communication packet is directly transmitted; a second fieldwhich stores address information indicating the second radiocommunication terminal as a final destination terminal; and a thirdfield which stores address information indicating the first radiocommunication terminal as a sending source.
 24. The radio communicationpacket according to claim 23, further comprising a fourth field whichstores address information indicating at least one radio communicationterminal from which the radio communication packet is directlytransmitted.
 25. The radio communication packet according to claim 23,wherein the address information stored in the second field includesgroup address information which contains at least one addressinformation.
 26. The radio communication packet according to claim 23,wherein the address information stored in the first field includes groupaddress information which contains at least one address information. 27.The radio communication packet according to claim 26, wherein groupaddress information contains broadcast address information in which noparticular address is specified.
 28. The radio communication packetaccording to claim 26, wherein group address information containsmulticast address information in which addresses assigned to a pluralityof candidate repeater stations are included.